The report by this international authority on the state and behaviour of the Earth’s atmosphere brought together scientific papers and reports from around the world, giving a single, consistent picture of 2013.

The statistics rolling out of the WMO report make sobering reading:

Globally, 2013 was the joint sixth-hottest year since records began in 1850.

Greenhouse gases driving the changes

Scientific attribution studies typically use climate models to determine the probability of extreme events occurring under different conditions. One way they do this is by modelling the atmosphere with and without greenhouse gas emissions.

By running these models many thousands of times, scientists can calculate how much the risk of extreme events has changed due to increased greenhouse gases generated by humans.

Using this kind of attribution approach, the record 2013 Australian temperatures were examined using a suite of climate model simulations, and the factors contributing to these extreme temperatures were identified. They were consistent with the influence of global warming.

We can even put a number on the increased likelihood. The WM0 report states that the probability of record hot summers like 2013 occurring across Australia increased by at least five times due to the effect of human greenhouse gas emissions.

Heatwaves are no exception

This study into extreme events in Australia doesn’t just tell us these events are already more likely because of climate change, but also that these warm years are expected to become even more frequent and severe.

And the scientific evidence keeps on coming.

Preliminary results of another study into Australian heatwaves show that the number of events we get every season is increasing and humans have contributed to this. During 2012-2013, Australia had its highest number of heatwaves since 1950, encompassing events during summer and autumn.

Research shows that human activity doubled the chance of this record number of heatwaves occurring in a single summer.

Under hypothetical conditions, in which humans have not added greenhouse gases to our atmosphere, the number of heatwaves we currently experience once every 60 years would only occur once every 120 years. In other words, humans have loaded the dice towards twice as many sixes being rolled.

Dangerous policy dismissal

It is dangerous that influential Australian politicians dismiss the role of climate change in recent extreme events.

In the aftermath of the unusually early New South Wales bushfires in October 2013, Prime Minister Tony Abbott dismissed the link between extreme fire conditions and climate change as “hogwash”. He then categorically rejected the idea that the fires were a function of climate change.

Pitiless blue sky

Dorothea Mackellar’s poem, My Country, published in 1908, talks of “droughts and flooding rains” and the “pitiless blue sky”, and is often used as the spurious basis for claiming that Australian extremes are just part of natural variation.

It suggests that if you can find a single similar event in our observed climate record, regardless of its timing, severity or frequency, then it must be nothing more than natural climate variation. Using this faulty reasoning, an out-of-season bushfire cannot be considered significant, and nor can the cascading temperature records of 2013 – despite the fact that they occurred during neutral El Nino Southern Oscillation conditions that normally produce milder conditions in Australia.

Not just guesswork

It is very unlikely that climate change will produce wholly new and wildly unexpected or exaggerated events, such as a 40°C day recorded on top of Mount Everest. That is not the way climate change works.

Rather, climate change will manifest itself in incremental shifts: changes in the timing of bushfire seasons; more severe, frequent or longer heatwaves; or temperature records that fall more often or by larger margins.

Unlike some policymakers, attribution studies don’t just guess whether global warming has influenced an observed extreme. Instead, the scientific approach requires a rigorous investigation of the factors that contribute to each event.

Attribution studies of recent extreme Australian fire weather are being conducted right now. However, the number of climate model experiments required to produce robust, scientifically valid results are many, so this will take time.

A recent preliminary analysis of the extreme Spring 2013 temperatures in New South Wales suggests these temperatures were made 15 times more likely because of the additional greenhouse gases we put into the atmosphere.

Let’s be clear here. Climate scientists also understand that high temperatures are only one factor that influences bushfires. However, the increase in hot temperatures already occurring in Australia throughout the year suggests, at the very least, that we should prepare ourselves for longer and more intense fire seasons.

Science shows extreme heat events are changing. It also shows a clear link between these extremes and climate change. If policymakers continue to ignore the science and deny these changes, we will be vastly unprepared for our future.

The WMO understands and values the science of event attribution and the insights it provides about our future. It is time our policymakers did the same.